* {
    margin: 0;
    padding: 0;
}
ul{
    list-style: none;
}
a{
    text-decoration: none;
}
img{
    vertical-align: middle;
}
body{
    background-color: #f5f5f5;
    margin: 0;  /* 补充body的默认边距重置 */
    padding: 0; /* 补充body的默认内边距重置 */
}